Electric current is not used up because electrons are not destroyed they transfer energy as they move round the circuit. This can happen in a resistor or light bulb when thermal energy and light energy are given out. Light bulbs produce light because they have high resistance and resist the flow of the electrons.
Series and parallel circuits
In diagram (a) current flows out of the battery through the ammeter and the bulbs, and as the electrons pass through the first bulb some energy is transferred. Then as the electrons pass through the second bulb, more energy is transferred.
The same number of electrons pass along the circuit so the current is the same at all points in the circuit.
In diagram (b) the current flows out of the cell around the circuit and splits between the two bulbs. The current is different in each bulb but the sum of the two currents = the current coming out of the battery.
Magnetism
Not all metals are magnetic. Only iron, steel, nickel and cobalt are magnetic.
One end of a magnet points towards the North, this is called the north-seeking pole. The other pole points towards the South and is called the south-seeking pole.
The Earth behaves like a huge magnet and a compass needle lines up with the lines of magnetic force. The region around the magnet is called a magnetic field. It can be shown using iron filings or a plotting compass.
An important rule of magnetism is: Like poles repel and unlike poles attract.
The real test for magnetism is to see if two magnets repel. If an object is made from iron, steel, cobalt or nickel then it will be attracted to a magnet, even if it is not itself magnetized.
Electromagnetism
When a current flows along a wire it causes a magnetic field around the wire.
Take the wire, wind it into a coil and you have a solenoid. Pass electricity through the coiled wire and you have a magnetic field similar to that produced by a bar magnet.
If you put a bar of iron inside the coil, it bahaves like a magnet - but only while the current is flowing. If the current is turned off, the bar stops being magnetic.
What you have now is an electromagnet.
An electromagnet is useful. The electric bell below uses an electromagnet to make it work. When the bell push, A, is closed, electric current can flow through the coil and the electromagnet, B, attracts the hammer, D.
The hammer is connected to a contact, C, and as the hammer moves it breaks the circuit and the electricity stops flowing. The springy metal, E, pulls the hammer back into its
Position. Another useful device using an electromagnet is a relay switch.